Discussion for Displacement Control Criteria of Soft Rock Tunnel in the Seismic Area

摘要

This paper studies on a certain highway project which passes through Longmen Shan fault zone, the one triggers 5.12 Wenchuan earthquakes directly. The region where the project resides is characterized by high percentage of soft rock mass, in particular the phyllite. Series of landslide have hitherto happened due to the instability of mountains along the highway which was caused by the great earthquake. Besides, since the phyllite-dominated rock was low-strength and easily soften by water, engineering disasters such as cave-in and large deformation of surrounding rock occurred frequently during the construction of tunnels located along the highway. The existing deformation control criteria fail gradually to fill the requirements of safe tunnelling. The author analyzed monitoring data from different tunnels with different cross-section types and different surrounding rock conditions, referred to relevant norms and eventually proposes new deformation control criteria based on allowable deformation and deformation rate.